1. Field of the Invention
This invention relates to a modified, thermosetting urea-formaldehyde resin composition useful for preparing a binder formulation, such as for making fiber mats, particularly glass fiber mats. The present invention also relates to a process of preparing the fiber mats using the binder formulation prepared with the resin composition and to the fiber mats prepared using the modified urea-formaldehyde resin composition in a binder formulation. In particular, the invention relates to a thermosetting urea-formaldehyde (UF) resin modified with styrene maleic anhydride at a particular binder viscosity and binder surface tension, with the resin composition being useful as a binder in roofing mats.
2. Description of Related Art
Glass fiber mats, fiber mats made from synthetic fibers and mats made from fiber blends find wide application in the building materials industry, for example, as insulation, as a substrate for making composite flooring, as a substrate for making siding (replacing similar sheets traditionally made using wood, cellulose or asbestos fibers), as substrate for printed circuit boards or battery separators, as filter stock, as tape stock, as reinforcement scrim in cementitious and non-cementitious coatings for masonry and as facing material for laminated articles such as foam composites and gypsum boards. One particular use is that in roofing mats for application in roofing shingles.
It is known to make reinforcing mats from glass fibers and to use these mats as substrates in the manufacture of a large number of roofing products such as shingles, built up roofing products, etc. Any known method of making nonwoven mats can be used, such as the conventional wet laid processes described in U.S. Pat. Nos. 4,112,174, 4,681,802 and 4,810,576, the disclosures of which are incorporated herein by reference. In these processes a slurry of glass fiber is made by adding glass fiber to a typical white water in a pulper to disperse the fiber in the white water forming a slurry having a fiber concentration of about 0.2-1.0 weight %, metering the slurry into a flow of white water and depositing this mixture on to a moving screen forming wire to dewater and form a wet nonwoven fibrous mat.
This wet nonwoven mat of glass fiber is then transferred to a second moving screen and run through a binder application saturating station where an aqueous binder mixture, such as an aqueous urea formaldehyde (UF) resin based binder mixture in water with about 24 weight percent, based on the dry weight of the UF resin, of a blend of 91.7 weight percent polyvinyl acetate homopolymer and 8.3 weigh percent of an acrylic tripolymer, is applied to the mat. This is followed by sucking off the excess binder and drying the unbonded, wet mat and curing (polymerizing) the UF based resin binder which bonds the fibers together in the mat. Preferably, the aqueous binder solution is applied using a curtain coater or a dip and squeeze applicator, but other methods of application such as spraying will also work.
In the drying and curing oven the mat is subjected to temperatures of 250-450 or 500 degrees F. for periods usually not exceeding 1-2 minutes and as little as a few seconds. Alternative forming methods include the use of well known processes of cylinder forming and “dry laying” using carding or random fiber distribution.
UF resins are most commonly used as a binder for fiber glass mats because of their suitability for the applications and their relatively low cost. Melamine formaldehyde resins are sometimes used for higher temperature applications. To improve the toughness of the mats, a combination of higher mat tear strength and mat flexibility, which is needed to permit higher processing speeds on roofing product manufacturing lines and for maximum roofing product performance on the roofs, it is common to modify or plasticize the UF resins as described above or with acrylic latexes or SBR latexes.
Because fiber mats made with an adhesive binder formulation consisting predominantly of a UF resin often are brittle, or because the strength properties of the mats may deteriorate appreciably subsequent to their preparation, especially when the mats are subjected to wet conditions, UF resin-based adhesive binder formulations have often been modified by fortifying the UF resin with a large amount of latex (emulsion) polymer, usually a polyvinyl acetate, vinyl acrylic or styrene-butadiene polymer, as noted above. Certain latexes have been shown to provide increased tensile strength and tear strength in the fiber mat. The use of styrene-butadiene latex-fortified, urea-formaldehyde resin compositions in preparing an adhesive binder formulation for making glass fiber mats is disclosed, for example, in U.S. Pat. Nos. 4,258,098; 4,560,612 and 4,917,764.
U.S. Pat. No. 4,917,764 highlights another problem sometimes encountered during the manufacture of fiber mats, especially when using the falling film curtain coater adhesive binder application technique. In particular, conventional UF resin-based adhesive binder formulations are sometimes deficient in providing an even deposition of the adhesive binder formulation on the mat. This uneven application of the adhesive binder formulation to the mat contributes to non-uniform mat properties.
It is an object of the present invention to overcome the foregoing problems associated with using urea-formaldehyde based binders in the preparation of glass mats.